Nanocrystals spark efficient
LEDs

Researchers from Los Alamos National Laboratory
have found a way to make highly efficient light-emitting diodes from nanocrystals,
or tiny bits of semiconductor.

The light-emitting diodes can be as small as a few nanometers
in diameter; a nanometer is one millionth of a millimeter, or the span
of 10 hydrogen atoms.

The nanoscale lights use very little power and can be made in
different colors simply by varying the sizes of the nanocrystals.

The microscopic light-emitting diodes could eventually be used
in nanoscale optics, including light-based computer chips. Large numbers
of the microscopic lights could also be used as ultra-high efficiency
lights, including street lighting, according to the researchers.

Nanocrystals are easy to manufacture, durable, and are very efficient
light emitters. The difficulty in using them as light sources is finding
a way to electrically excite the crystals to kick off the light-emission
process. This is because nanocrystals have an insulating shell of molecules.
Previous efforts used organic conductors to excite the nanocrystals, but
were not very efficient.

The researchers' method uses a quantum well, or electron trap,
to inject pairs of electrons and their charge opposite, holes, into the
nanocrystals. Electrons and holes pair up, annihilate each other, and
the resulting energy is released as photons.

The technology could become commercially viable in three to five
years, according to the researchers. The work appeared in the June 10,
2004 issue of Nature.